Wavelength selective radiation sensor

ABSTRACT

There may be provided a radiation sensor, that may include multiple semiconductor regions that form a sensing PN junction and a draining PN junction that is located below the sensing PN junction; a bias circuit that is configured to (i) bias the sensing PN junction to maintain a sensing PN junction depletion region of a fixed size during a first sensing period and during a second sensing period, and (i) bias the draining PN junction to form a draining PN junction depletion region of a first size during the first sensing period and of a second size during the second sensing period; and an output circuit that is configured to generate a first output signal that represent sensed radiation out of radiation that impinged on the radiation sensor during the first sensing period, and to generate a second output signal that represent sensed radiation out of radiation impinged on the radiation sensor during the second sensing period.

BACKGROUND OF THE INVENTION

Ultraviolet (UV) sensors are used for measuring UV light intensity, andfor analyzing the power in three different UV bands—UVA, UVB and UVC.UVA rays have the shortest wavelength, followed by UVB and UVC.

Silicon sensors have small response in the UV, mainly because of UVblocking layers (nitride layers in the Backend) and due to very shallowabsorption depth.

Silicon sensors have much stronger absorption in the visible lightrange. Furthermore, most of the power of sunlight is in the visiblewavelength range

Visible-blind sensor may be provided, for instance GaN sensors, however,those are very expensive and still fail to properly analyze thecomposition of the UV radiation—especially separate between UVA, UVB andUVC.

There is a growing need to provide a radiation sensor that is radiationselective.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is an example of a radiation sensor;

FIG. 2 is an example of a radiation sensor;

FIGS. 3 and 4 illustrate examples of distribution of photogeneratedcarriers;

FIG. 5 illustrates example of timing diagrams;

FIG. 6 is an example of a radiation sensor; and

FIG. 7 is an example of a method.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings.

Because the illustrated embodiments of the present invention may for themost part, be implemented using electronic components and circuits knownto those skilled in the art, details will not be explained in anygreater extent than that considered necessary as illustrated above, forthe understanding and appreciation of the underlying concepts of thepresent invention and in order not to obfuscate or distract from theteachings of the present invention.

FIG. 1 illustrates an example of a radiation sensor 10 that includesmultiple semiconductor regions 41, 42, 43 and 44, a bias circuit 19,controller 18, and output circuit 20. Controller 18 may control the biascircuit 19 and the output circuit 20.

Multiple radiation sensors may be provided—and may share theircontroller 18 and their bias circuit 19.

The multiple semiconductor regions form a sensing PN junction 51 and adraining PN junction 52. The draining PN junction 52 is located belowthe sensing PN junction 51.

The multiple semiconductor regions may include, for example, a firstsemiconductor region 41 of an N-type, a second semiconductor region 42of a P-type, and a third semiconductor region 43 of an N-type.Alternatively—the multiple semiconductor regions may include, forexample, a first semiconductor region of a P-type, a secondsemiconductor region of an N-type, and a third semiconductor region of aP-type.

In both cases—the sensing PN junction 45 is formed between the firstsemiconductor region 41 and the second semiconductor region 42. Thedraining PN junction 52 is formed between the second semiconductorregion 42 and the third semiconductor region 43. The third semiconductorregion 43 may be located above substrate 44 or any other part ofsemiconductor unit 40.

The bias circuit 19 is configured to bias the sensing PN junction toform a sensing PN junction depletion region of a fixed size duringmultiple sensing periods—for example during a first sensing period andduring a second sensing period. This may be obtained by providing afixed value Vsense 31 during the multiple sensing periods. Vsense may beprovided to the first semiconductor region. The first semiconductorregion may also be in communication with the output circuit 20 and mayfeed the output circuit 20 with current indicative of radiation.

The bias circuit 19 is also configured to bias the draining PN junctionto form a draining PN junction depletion region of different sizesduring multiple sensing periods (while maintaining the same size duringa single sensing period). For example—the bias circuit 19 may bias thedraining PN junction to have a draining PN junction depletion region ofa first size during the first sensing period and to have a draining PNjunction depletion region of a second size during the second sensingperiod, the first size differ from the second size. Vscan 23 may beprovided to the third semiconductor region 43.

The first semiconductor region may have a top surface located within acertain plane 15. [Amos]—I'm not sure what his plane refers to, and Icant find plane 15 in the drawings

A first portion 42(1) of the second semiconductor region may be locatedbelow the first semiconductor region 41. A second portion 42(2) of thesecond semiconductor region may reach the certain plane 15. The firstportion 42(1) of the second semiconductor region may be parallel to thecertain plane and be positioned directly below the first semiconductorregion. The second semiconductor region may at least partially surroundthe first semiconductor region.

A first portion 43(1) of the third semiconductor region may be locatedbelow the second semiconductor region 42—or at least below the firstportion 42(1) of the second semiconductor region. A second portion 43(2)of the third semiconductor region may reach the certain plane 15. Thefirst portion of the third semiconductor region may be parallel to thecertain plane and be positioned directly below the first portion of thesecond semiconductor region. The third semiconductor region may at leastpartially surround the second semiconductor region.

FIG. 2 illustrates examples of depletion regions formed in thesemiconductor unit during a first sensing period (Vramp has a firstvalue Vramp1), and the depletion regions formed in the semiconductorunit during a second sensing period (Vramp has a second value Vramp2).Vramp2 exceeds Vramp1.

Because Vsense remains the same—the size of sensing PN junctiondepletion region 45 remains the same. Because Vramp2 exceeds Vramp1 thedraining PN junction depletion region 46 of the first sensing period issmaller than the draining PN junction depletion region 46 during thesecond sensing period.

Radiation of different wavelengths exhibit different penetration depthswithin the semiconductor unit 40—and accordingly result in the formationof photogenerated carriers at different depths (distance from thecertain region 15) within the semiconductor unit 40.

Any photogenerated carrier formed within the semiconductor unit may be asensed photogenerated carrier or a drained photogenerated carrier.Sensed photogenerated carriers reach the first semiconductor region andbe sensed by the output circuit. Drained photogenerated carriers do notreach the first semiconductor region.

Sensed photogenerated carriers may be formed within the sensing PNjunction depletion region 45. Drained photogenerated carriers may beformed within the draining PN junction depletion region 46.

Photogenerated carriers that are formed between the sensing PN junctiondepletion region 45 and the draining PN junction depletion region 46 maybe distributed to provide some sensed photogenerated carriers and somedrained photogenerated carriers. The distribution depends, at least, onthe location of the photogenerated carriers from each of the depletionregions.

FIGS. 3 and 4 illustrate examples of distributions of photogeneratedcarriers 63 between the sensing PN junction depletion region 45 and thedraining PN junction depletion region 46—at two different values ofVramp and under different illumination conditions. FIG. 3 illustrates adistribution when illuminating the semiconductor unit with firstwavelength radiation 61. FIG. 3 illustrates a distribution whenilluminating the semiconductor unit with second wavelength radiation 62.

The semiconductor unit may be fabricated to correspond with thepenetration depth of radiation:

-   -   a. Have a structure and size (for example a structure and size        of the first semiconductor region) that corresponds to the        penetration depth of a first wavelength radiation—so that most        or all of the photogenerated carriers that are generated due to        the first wavelength radiation to reach the first semiconductor        region and not reach the draining PN junction.    -   b. Have a structure and size (for example a structure and size        of the third semiconductor region) that corresponds to the        penetration depth of a second wavelength radiation—so that most        or all of the photogenerated carriers that are generated due to        the second wavelength radiation to reach the third semiconductor        region and reach the draining PN junction.

The first wavelength radiation may be of more significance than thesecond wavelength radiation—but this is not necessarily so. The secondwavelength radiation may be insignificant—and may be filtered out. Forexample—be visible light radiation—when trying to sense ultravioletradiation.

The mentioned above radiation sensor may exhibit a sensitivity to firstwavelength radiation that is a function of a size of the sensing PNjunction depletion region, and may exhibit a sensitivity to secondwavelength radiation that is a function of a size of the draining PNjunction depletion region.

Maintaining a fixed size of sensing PN junction depletion region whilechanging the size of the draining PN junction depletion region allows todistinguish between the first wavelength radiation and the secondwavelength radiation.

The sensing unit may be operated by having multiple sensing period inwhich different Vramp value are applied and the same Vsense isapplied—thereby providing multiple measurements that may be analyzed inorder to distinguish between multiple spectral components (of differentwavelengths) of impinging radiation. Increasing the absolute value ofVramp may cut more portions of the longer wavelength radiation.

By controlling the depth of the depletion regions by biasing—themeasurements may be less dependent to (and even ignorant of) processvariations. Additionally or alternatively—a mapping between radiationproperties (intensity and wavelength) and process variation may beobtained (generated or received) and may be used to compensate forprocess variations. The mapping may include illuminating with radiationof known properties (intensity and radiation) of sensing units ofdifferent process flavors.

The first wavelength and the second wavelength may be any pair ofdifferent wavelengths—for example two different ultraviolet wavelengths,visual light and ultraviolet radiation, two non-ultraviolet radiations,and the like.

FIG. 5 illustrates timing diagrams 65 and 66.

Timing diagram 65 illustrates the value of Vsense 31—which is the sameduring first to fourth (SP1-SP4) sensing periods 71-74.

Timing diagram 66 illustrates the value of Vscan 32—which changesbetween the first to fourth (SP1-SP4) sensing periods 71-74.

FIG. 6 illustrates an example of a radiation sensor 10 that includesmultiple semiconductor regions 41, 42, 43 and 44, a bias circuit 19,controller 18, and output circuit 20.

The output circuit 10 is illustrated being a capacitive transimpedanceamplifier that includes input node 27, output node 28, operationalamplifier 23, switch 21 and capacitor 22. Operational amplifier 23includes a non-inverting input port 25, an inverting input port 24 andan output port 26.

The capacitor 22 and the switch 21 are coupled between an input node 27and the output node 28. The input node is also connected to theinverting input port 24. The output node 28 is also connected to theoutput port 26.

The non-inverting input port 25 is biased with a fixed bias signalVsense 31. The inverting input port 24 is also coupled to firstsemiconductor region 41. Due to the virtual ground between thenon-inverting input port 25 and the inverting input port 24—the firstsemiconductor region 41 is fed with Vsense 31. The output port 26 isconnected to output node 28 that provides output signal Vout 28.

Assuming that the photogenerated carriers are electrons—during a sensingperiod switch 21 is open and current generated by sensed photogeneratedcarriers charge capacitor 22. The sensing period may also be referred toas an integration period.

When the sensing period ends the voltage on capacitor 22 reflects thecurrent that charged the capacitor 22.

At the end of the sensing period the switch closes and the capacitor isdischarged.

FIG. 7 illustrates an example of method 100.

FIG. 100 may start by steps 110, 120 and 130.

Step 110 may include receiving radiation sensor during multiple sensingperiods. The radiation sensor may include (a) multiple semiconductorregions that form a sensing PN junction and a draining PN junction thatis located below the sensing PN junction, (b) a biasing circuit, and anoutput circuit.

Step 120 may include biasing, by the bias circuit and during themultiple sensing periods, the sensing PN junction to maintain a sensingPN junction depletion region of a fixed size during each sensing period.The biasing may include changing a biasing between one sensing period toanother sensing period.

Steps 110 and 120 may be followed by step 130 of generating, by theoutput circuit, multiple output signals indicative of radiation receivedduring the multiple sensing periods.

Any reference to any of the terms “comprise”, “comprises”, “comprising”“including”, “may include” and “includes” may be applied to any of theterms “consists”, “consisting”, “consisting essentially of”. Forexample—any of the rectifying circuits illustrated in any figure mayinclude more components that those illustrated in the figure, only thecomponents illustrated in the figure or substantially only thecomponents illustrate din the figure.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims.

Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under”and the like in the description and in the claims, if any, are used fordescriptive purposes and not necessarily for describing permanentrelative positions. It is understood that the terms so used areinterchangeable under appropriate circumstances such that theembodiments of the invention described herein are, for example, capableof operation in other orientations than those illustrated or otherwisedescribed herein.

Those skilled in the art will recognize that the boundaries betweenlogic blocks are merely illustrative and that alternative embodimentsmay merge logic blocks or circuit elements or impose an alternatedecomposition of functionality upon various logic blocks or circuitelements. Thus, it is to be understood that the architectures depictedherein are merely exemplary, and that in fact many other architecturescan be implemented which achieve the same functionality.

Any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality.

Furthermore, those skilled in the art will recognize that boundariesbetween the above described operations merely illustrative. The multipleoperations may be combined into a single operation, a single operationmay be distributed in additional operations and operations may beexecuted at least partially overlapping in time. Moreover, alternativeembodiments may include multiple instances of a particular operation,and the order of operations may be altered in various other embodiments.

Also for example, in one embodiment, the illustrated examples may beimplemented as circuitry located on a single integrated circuit orwithin a same device. Alternatively, the examples may be implemented asany number of separate integrated circuits or separate devicesinterconnected with each other in a suitable manner.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the terms “a” or “an,” as used herein, are definedas one or more than one. Also, the use of introductory phrases such as“at least one” and “one or more” in the claims should not be construedto imply that the introduction of another claim element by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim element to inventions containing only one suchelement, even when the same claim includes the introductory phrases “oneor more” or “at least one” and indefinite articles such as “a” or “an.”The same holds true for the use of definite articles. Unless statedotherwise, terms such as “first” and “second” are used to arbitrarilydistinguish between the elements such terms describe. Thus, these termsare not necessarily intended to indicate temporal or otherprioritization of such elements.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

What is claimed is:
 1. A radiation sensor, comprising: multiplesemiconductor regions that form a sensing PN junction and a draining PNjunction that is located below the sensing PN junction; a bias circuitthat is configured to (i) bias the sensing PN junction to maintain asensing PN junction depletion region of a fixed size during a firstsensing period and during a second sensing period, and (i) bias thedraining PN junction to form a draining PN junction depletion region ofa first size during the first sensing period and of a second size duringthe second sensing period; wherein the first size differs from thesecond size; and an output circuit that is configured to generate afirst output signal that represent sensed radiation out of radiationthat impinged on the radiation sensor during the first sensing period,and to generate a second output signal that represent sensed radiationout of radiation impinged on the radiation sensor during the secondsensing period.
 2. The radiation sensor according to claim 1 wherein thesensing PN junction depletion region and the draining PN junctiondepletion region are formed within a same semiconductor region of themultiple semiconductor region.
 3. The radiation sensor according toclaim 2 wherein at least a part of the sensing PN junction depletionregion is positioned above at least a corresponding part of the drainingPN junction depletion region.
 4. The radiation sensor according to claim1 wherein a sensitivity of the radiation sensor to radiation of a firstwavelength is a function of a size of the sensing PN junction depletionregion; and wherein a sensitivity of the radiation sensor to radiationof a second wavelength is a function of a size of the draining PNjunction depletion region.
 5. The radiation sensor according to claim 4wherein the first wavelength and the second wavelength are differentultraviolet wavelengths.
 6. The radiation sensor according to claim 1wherein the output circuit comprises a capacitive transimpedanceamplifier.
 7. The radiation sensor according to claim 6, wherein thecapacitive transimpedance amplifier comprises an operational amplifier,a switch and a capacitor; wherein the operational amplifier comprises annon-inverting input port, an inverting input port and an output port;wherein each one of the capacitor and the switch are coupled between theinverting input port and the output port; wherein the non-invertinginput port is biased with a fixed bias signal; and wherein the invertinginput port is also coupled to a first semiconductor region of themultiple semiconductor regions.
 8. The radiation sensor according toclaim 1 wherein the multiple semiconductor regions comprise a firstsemiconductor region of an N-type, a second semiconductor region of aP-type, and a third semiconductor region of an N-type, wherein thesensing PN junction is formed between the first semiconductor region andthe second semiconductor region, and wherein the draining PN junction isformed between the second semiconductor region and the thirdsemiconductor region.
 9. A method for sensing radiation, the methodcomprises: receiving radiation by a radiation sensor during multiplesensing periods; wherein the radiation sensor comprises (a) multiplesemiconductor regions that form a sensing PN junction and a draining PNjunction that is located below the sensing PN junction, (b) a biasingcircuit, and an output circuit; biasing, by the bias circuit and duringthe multiple sensing periods, the sensing PN junction to maintain asensing PN junction depletion region of a fixed size during each sensingperiod; wherein the biasing comprises changing a biasing between onesensing period to another sensing period to provide a draining PNjunction depletion region of different sizes during different sensingperiods of the multiple sensing periods; and generating, by the outputcircuit, multiple output signals indicative of the radiation receivedduring the multiple sensing periods.
 10. The method according to claim 9wherein the sensing PN junction depletion region and the draining PNjunction depletion region are formed within a same semiconductor regionof the multiple semiconductor region.
 11. The method according to claim10 wherein at least a part of the sensing PN junction depletion regionis positioned above at least a corresponding part of the draining PNjunction depletion region.
 12. The method according to claim 9 wherein asensitivity of the radiation sensor to radiation of a first wavelengthis a function of a size of the sensing PN junction depletion region; andwherein a sensitivity of the radiation sensor to radiation of a secondwavelength is a function of a size of the draining PN junction depletionregion.
 13. The method according to claim 12 wherein the firstwavelength and the second wavelength are different ultravioletwavelengths.
 14. The method according to claim 9 wherein the outputcircuit comprises a capacitive transimpedance amplifier.
 15. The methodaccording to claim 14 wherein the capacitive transimpedance amplifiercomprises an operational amplifier, a switch and a capacitor; whereinthe operational amplifier comprises an non-inverting input port, aninverting input port and an output port; wherein each one of thecapacitor and the switch are coupled between the inverting input portand the output port; wherein the non-inverting input port is biased witha fixed bias signal; and wherein the inverting input port is alsocoupled to a first semiconductor region of the multiple semiconductorregions.
 16. The method according to claim 9 wherein the multiplesemiconductor regions comprise a first semiconductor region of anN-type, a second semiconductor region of a P-type, and a thirdsemiconductor region of an N-type, wherein the sensing PN junction isformed between the first semiconductor region and the secondsemiconductor region, and wherein the draining PN junction is formedbetween the second semiconductor region and the third semiconductorregion.